In a liquid chromatograph apparatus of one kind of a liquid sample analyzing apparatus, a mobile phase is sucked into the apparatus by a pump unit, being fed to a separation column with a sample introduced by an automatic sample introduction unit. The sample introduced in the separation column is separated into components to be detected by various kinds of detectors. Generally, in a field of an apparatus so called a high performance liquid chromatography (HPLC), an analysis operation is required to be operated under high pressure flow passage at 20 to 40 M Pa at its maximum. In a pump unit used for HPLC as described above, it is required that a mobile phase can be supplied to the apparatus correctly and precisely even under high pressure condition.
Further, the automatic sample introducing unit is used as an apparatus which sucks the sample liquid by using a needle from a sample holding container lined up on sample rack, thereafter, the apparatus stores the sample in a sample storage loop to discharge the sample into a mobile phase flow passage of the liquid chromatography automatically. Furthermore, there are automatic sample introduction units having a pre-processing function for diluting a sample before discharging into mobile phase flow passage and for mixing the sample and reaction reagent for labeling, or the like.
The injection system in the above automatic sample introduction apparatus is generally divided into two kinds. In one kind of an injection system which is a direct injection system (refer to the patent document 1 and the patent document 2), a needle and a sample storage loop are integrated into a mobile phase flow passage under high pressure condition. In the other kind of an injection system which is a loop injection system (refer to the patent document 3), only a needle is integrated into a mobile phase flow passage under high pressure condition.
In the direct injection system, a sample temporarily stored in the needle and the sample storage loop is pushed out toward the column by the mobile phase at the start of analysis, and the mobile phase is always flushed in the needle and the sample storage loop during the analysis operation, so that the sucked sample can be introduced into the column without waste of the sample, and the is no need for installing other unit for washing the inner of the needle contaminated by the sample. It is the merit of the direct injection system.
On one hand, since the needle is integrated into one part of the mobile phase flow passage in principle, a construction is required for keeping the fluid-tight between the needle and the sample injection port under the high pressure condition. Accordingly, the direct injection system is not suitable for handling of diluting and mixing the sample in the pre-process. It is the demerit of the direct injection system.
On the other hand, according to the loop injection system, since the needle is positioned outside of the mobile phase flow passage under high pressure condition during the analysis operation, the movement of the needle and the sample accounting operation can be executed during the analysis operation. Accordingly, a construction is not required for keeping the high pressure between the needle and the sample injection port, so that the pre-process of the sample can be executed during the analysis operation. It is the merit of the loop injection system. However, the loop injection system requires an equipment and process for washing the inner of the needle, so that the loop injection system may require long time for injecting a sample in comparison with the direct injection system. It is the demerit of the loop injection system.
Recently, so called an ultra high performance liquid chromatography (UHPLC) is rapidly advanced by the advance of the column bulking agent refine technologies. In the UHPLC, an analysis operation is executed under 60 to 120 M Pa at its maximum, the analysis time per one sample is several ten seconds to several minutes which are one per several times of the conventional HPLC, so that the through put of an analysis operation can be improved remarkably.
The basic item of an automatic sample introducing unit required for the UHPLC is to have high injection quantity repeatability, low carry over, high speed process (reducing of cycle time), high reliability, and high durability against multiple samples analysis request under ultra high pressure of 60 to 120 M Pa at its maximum.
In general, a sample introduction apparatus employing the direct injection system has a mechanism which can always keep the fluid-tight between the needle and the seal in the sample injection port in order to avoid the ejection of the mobile phase form the sample inlet port even under high pressure condition. During the analysis operation, the needle integrated in the high pressure flow passage and the sample storage loop are separated from the high pressure flow passage by the flow passage exchange valve at the sample suction step, the needle and the solvent in the sample storage loop being exposed under the atmospheric pressure.
Further, after the needle and the solvent are exposed under the atmospheric pressure, the needle is inserted into the sample hold container, and the sample is sucked into the needle or sample storage loop, thereafter, the needle is moved at the above-mentioned sample injection port. At this step, the flow passage exchange valve is switched again, the sample with the mobile phase fed by the pump units are supplied to the column.
In the UHLPC, several times sample processing ability is required under the several times ultra high pressure in comparison with the HPLC. Namely, a complex construction and several times durability are required for keeping the fluid-tight between the needle and the sample injection port under 60 to 120 M Pa condition. It is difficult to realize the above-mentioned construction.
Further, in the UHPLC, since the analysis time per one sample is short time of several ten seconds to several minutes, it is difficult to fully execute the flushing operation of the mobile phase in the needle. Namely, it is difficult for reducing the carry over of a sample due to the principle of the UHPLC.
Therefore, the automatic sample introduction unit of the loop injection system is suitable for the UHPLC.